One of techniques for preserving foods, pharmaceutical products and the like is preservation utilizing oxygen absorbing agents (oxygen scavengers) that remove oxygen in an atmosphere. Specifically, the preservation utilizing oxygen absorbing agents is a technique in which an oxygen scavenger capable of absorbing oxygen in atmosphere, together with an object, is placed and hermetically sealed in a packaging body. A technique that has recently become used is that a deterioration in an object within a packaging body by oxygen is suppressed without enclosing an oxygen absorbing agent by imparting an oxygen absorbing capability to the packaging body per se. The packaging body having the oxygen absorbing capability is prepared by extruding a resin composition including an oxygen absorbing agent incorporated in a thermoplastic resin commonly used as a material for packaging body materials into a film or sheet that is then formed into a packaging body.
In addition to conventional inorganic main agents such as iron powders and sulfites and organic main agents such as L-ascorbic acid and erythorbic acid, oxygen absorbing agents that do not require water in oxygen absorption have recently become used. Such oxygen absorbing agents include, for example, oxygen scavengers including cerium oxide utilizing oxygen defects as a main agent (for example, Japanese Patent Application Laid-Open No. 185653/2007, International Publication No. 099935/2008, and International Publication No. 133057/2008), oxygen scavengers including titanium oxide containing oxygen defects as a main agent (for example, Japanese Patent Application Laid-Open No. 104064/2005), oxygen scavengers including a metal subjected to hydrogen reduction as a main agent (for example, Japanese Patent Application Laid-Open No. 277148/1987), and oxygen scavengers that utilize autoxidation of organic substances. These oxygen absorbing agents are directly reacted with oxygen without through water to absorb oxygen within the packaging body and thus are suitable for preservation for antirust purposes of pharmaceuticals or dried foods that require use or preservation under dry conditions, or metallic products that are damaged by water or moisture.
On the other hand, the above oxygen absorbing agents are directly reacted with oxygen in an atmosphere and thus, when stored in air, are likely to suffer from a safety problem, for example, a deterioration in an oxygen absorbing capability with the elapse of time or spontaneous ignition in air in an extreme case as a result of a reaction with oxygen in air. For this reason, the oxygen absorbing agents are in many cases used in the form of a dispersion of the oxygen absorbing agents in resins. In the dispersion of oxygen absorbing agents in resins, however, the oxygen absorbing agents are disadvantageously reacted with oxygen in an atmosphere, and, thus, a method should be adopted in which oxygen absorbing agents are added to resins in an inert gas or in vacuo or in which, when oxygen absorbing agents are added to resins, the activity of the oxygen absorbing agents is temporarily lowered. For example, Japanese Patent Application Laid-Open No. 185653/2007 proposes that a reaction with oxygen in an atmosphere is suppressed by lowering the specific surface area of oxygen scavenger particles. Further, International Publication No. 099935/2008 proposes that active sites of oxygen absorbing agents reactive with oxygen are closed by carbon dioxide followed by dispersion in resins. Furthermore, International Publication No. 133057/2008 proposes that antioxidants are added to resins in a nitrogen atmosphere.